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Acids and Bases

Acids and Bases. Acidity, Basicity, and pH. Self-Ionization of Water. Water is both an acid and a base. We call this __________________. By the Br Ø nsted -Lowry definition, this means that water can donate a proton AND accept a proton.

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Acids and Bases

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  1. Acids and Bases Acidity, Basicity, and pH

  2. Self-Ionization of Water • Water is both an acid and a base. We call this __________________. • By the BrØnsted-Lowry definition, this means that water can donate a proton AND accept a proton. H2O(l) + H2O(l) H3O+(aq) + OH-(aq) • This process is known as the self-ionization of water.

  3. Concentration of Water • The self-ionization of water makes even pure water have ions within it. • In pure water, the two ions (acidic and basic) must share the same concentration (1:1 ratio) • Experiments show that this concentration is 1.00x10-7 M at 25°C. [H3O+] = [OH-] = 1.00x10-7 M

  4. Concentration of Water

  5. Equilibrium Constant • The equilibrium constant is an expression that relates the concentrations of species involved in an equilibrium. • To write an equilibrium constant expression, you must know the concentrations of the products and the reactants at equilibrium. Keq = [Products] / [Reactants] **Excluding solids and liquids

  6. Equilibrium Constant • Consider the equilibrium of water: H2O(l) + H2O(l) H3O+(aq) + OH-(aq) 2H2O(l) H3O+(aq) + OH-(aq) • This equation’s Equilibrium Constant is: Keq = (1.00x10-7)(1.00x10-7) = 1.00x10-14 • This is a special equilibrium constant, known as Kw

  7. Self-Ionization Constant of Water • Keq = (1.00x10-7)(1.00x10-7) = 1.00x10-14 • This is the Self-Ionization Constant of Water • Known as Kw • We can use this information about water and the relationship of hydronium and hydroxide to figure out various concentrations in solutions [H3O+][OH-] = Kw = 1.00x10-14

  8. Practice • What is [OH-] in a 3.00x10-5 M solution of HCl? • HCl = a strong acid or a strong base? • So, is this a hydroxide conc or a hydronium conc? • Since this is a strong acid it completely ______________, implying that [HCl] = [H3O+] • Remember the self-ionization constant of water • Kw = [H3O+][OH-] = 1.00x10-14 • Plug in your variables and calculate what your are asked to find.

  9. Practice • What is [OH-] in a 3.00x10-5 M solution of HCl? Kw= [H3O+][OH-] = 1.00x10-14 1.00x10-14 = (3.00x10-5M)[OH-] 1.00x10-14 = [OH-] 3.00x10-5M [OH-] = 3.33x10-10 M

  10. pH • A solution is neutral when the concentration of hydroxide is exactly equal to the concentration of the hydronium. pH = 7 • If the conc of the hydronium is stronger than the conc of the hydroxide than the solution with have a pH of <7. • If the conc of the hydroxide is stronger than the conc of the hydronium than the solution with have a pH of >7.

  11. pH • The pH is a value used to express the acidity or alkalinity of a solution; it is defined as the logarithm of the reciprocal of the concentration of hydronium ions. • p = power, H = hydrogen • pH = power of hydrogen pH = -log[H3O+] [H3O+] = 10-pH

  12. pH Scale • pH is a logarithmic scale, meaning an increase in a value is an increase of 10x • i.e. A solution whose pH is 2.0 has a [H3O+] that is 10x greater than a solution whose pH is 3.0 and a 100x greater than a solution whose pH is 4.0

  13. Practice #1 • What is the pH of the following solutions: • 0.00010 M solution of HNO3? • 0.0136 M solution of KOH?

  14. Practice #2 • What are the concentrations of the hydronium and hydroxide ions in a sample of rain that has a pH of 5.05? Gather info: pH = 5.05 Kw = 1.00x10-14 [H3O+] = ? [OH-] = ? • Plan your work

  15. Measuring pH • Method #1 • Uses indicators • Quick and simple • Does not, however, give very precise results • Method #2 • Uses a pH meter • Very precise • More complicated and expensive

  16. Measuring pH • Certain dyes with change different colors in solutions of different pH • These dyes are known as indicators. • A compound that can reversibly change color depending on the pH of the solution or other chemical change. • The color after the addition of the indicator can help determine the relative pH of the solution.

  17. Litmus Paper • Litmus is a dye used as an indicator that is soaked into filter paper • It serves as a quick, cheap, convenient check of a solution’s pH. • Blue Litmus Paper – Turns red under acidic conditions • Red Litmus Paper – Turns blue under basic conditions

  18. Measuring pH • pH meters are a probe that is submerged into a solution. • An electrical voltage develops between two electrodes and the probe digitally reads out a pH value. • The voltage is a measure of the conductivity of the hydronium solution.

  19. Homework • Page 547, # 1, 2, 5, 6, 7, 8, 9, 10 • Due tomorrow!! • Vocab also due on Wednesday.

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